distribution, &c. of the magnetic intensity in ships of war. 349 
intensity at the same point, appear to be proportional to the 
alteration in the direction of the ship's head. Such inequalities 
must however be considered as necessary consequences of the 
irregular distribution of the iron, and of its inequality of 
action. 
The position of the common centre of force of all the de- 
termined intensities may be referred to the three rectangular 
co-ordinate planes, by the same method as that employed 
for the Scylla ; and the application of the different numerical 
elements to the proper formula, furnishes the following 
results : 
Value of S" V", being the 
Distance of the Centre 
of Force from the Hori- 
zontal co-ordinate plane. 
Value of S" W", being the 
Distance of the Centre of 
Force from the Longitu- 
dinal co-ordinate plane. 
Value of S" T", being the 
Distance of the Centre of 
Force from the Trans- 
verse co-ordinate plane. 
9-45 
16.08 
59-81 
By comparing these results with the actual dimensions of 
the ship, it appears that the common centre of force of all 
the intensities is at the point S", 59.8 1 feet from the trans- 
verse co-ordinate plane near the fore part of the main-mast, 
and 4.71 feet abaft the prolongation of the after part of the 
shot-locker. From the horizontal co-ordinate plane the 
same point appears to be 9.45 feet distant, and hence 1.25 
feet above the plane of the main deck. Its distance also from 
the longitudinal co-ordinate plane is .08 feet on the starboard 
side ; and practically considered, may be regarded as in the 
middle section of the ship. 
Of the Impregnable of 104 guns. 
Many interesting results were obtained on the different 
decks of this fine ship. Three longitudinal planes, similar to 
